1. Field of the Invention
The present invention relates in general to a gas seal and support for a rotating semiconductor processor and, more particularly, to a gas seal and support for a rotating rinser-dryer system.
2. Description of the Prior Art
In the production of integrated circuits, circular wafers or substrates are processed through multiple steps before being cut into segments to form the integrated circuits. The semiconductor wafers are typically circular in shape, and generally 0.02 to 0.04 inch thick, from 6 to 12 inches in diameter, and made of silicon. Accordingly, the large, thin wafers are very fragile.
The deposition of materials upon these fragile substrates requires that the semiconductors be coated with numerous solutions and then rinsed and dried. For example, processing can include steps in which layers of material are masked, deposited, processed, etched, polished or various combinations of these steps. It is important that the wafers remain extremely clean during these various processing steps. To remove undesired chemicals between various processing steps, the semiconductors often undergo a rinsing and drying cycle during which a plurality of wafers are placed in a wafer carrier, rotated, and sprayed with processing fluids during the rotation. It is important during these processing steps that the wafer handling neither damage the wafers or the circuits being formed on the wafers, nor introduce any particles or contaminants. Vibration of the wafers and wafer carrier is one major source of movement that can generate particles. There is thus a need for a semiconductor processor that controls vibration to reduce particle generation.
Contaminants can also be created when rotating wafer carriers contact adjacent structure, or when the drive shaft that rotates the wafer carriers contacts any adjacent structure. Any contact between the rotating drive shaft and the stationary bowl or chamber enclosing the wafer carrier, can cause particle generation which contaminates the semiconductors. Initially, low friction ferro-fluidic seals were used to reduce contaminants from the rotating shaft seal, but they proved inadequate as the size of the circuitry became smaller and the size and number of permissible contaminants became smaller.
In some cases, combinations of contacting and noncontacting seals were used, as well as noncontacting pressurized gas seals. But these noncontacting gas seals are characterized by relatively large sealing areas between the bowl and the motor shaft. Alternatively, if the seal is placed along the length of the shaft then the gap between the rotating shaft and adjacent structure must accommodate shaft motion. Small spacings between parts conserves gas usage, but generates particles when the rotating shaft contacts the stationary processing bowl. If the gap is made larger, then gas pressure and gas consumption increases which adds significant cost to the use of these processing systems. There is thus a need for a gas pressurized, noncontacting seal that has a close spacing to reduce gas consumption, but which accommodates movement of the rotating shaft.
Another problem with rotating processing systems is the vibration caused by the rotating motor, shaft and wafer carrier inside a stationary bowl or chamber. For a variety of reasons the rotating wafers and wafer carrier are typically not balanced, and that unbalance generates vibration. Sometimes wafers are offset from the center of rotation in order to seat the wafers against the carrier. Sometimes different numbers of wafers are placed in the carrier. Sometimes parts bend and cause an imbalance. In all cases, the vibration can cause undesirable movement that generates contaminants.
Further, the vibration of these rotating parts can adversely affect not only the wafers within the processing chamber, but adjacent machinery used in the manufacture of the semiconductors. There is thus a need for a rotating processor that reduces the vibration transmitted to adjacent equipment.
In particular, a need exists for a rotating processor that uses a noncontacting seal with a small sealing area and low gas consumption, and which further reduces the undesirable transmission of vibrations to adjacent equipment.